Possible evidence for the stabilization of β-carbon nitride by high-energy ball milling

The possibility of stabilizing the theoretically predicted beta-C3N4 phase by high-energy ball milling is investigated. Charges of graphitic carbon were milled with and without minor alloying additions under different atmospheric media, namely gas and/or liquid phases of nitrogen, air, or ammonia. Milling was performed at either of two energy levels for periods of up to 48 h, The beta-C3N4 phase was found to exist as small crystallites in a matrix of primarily amorphous carbon at volume fractions estimated between 5 and 10 at.%. High-resolution electron diffraction and x-ray diffraction indicate that the crystalline nature of the C3N4 phase corresponds with a hexagonal lattice with a = 6.46 Angstrom and c/a = 0.374, which are within 2% of the theoretically calculated lattice parameter values. Analysis of electron energy-loss spectroscopy (EELS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectra verify the presence of chemically bonded carbon and nitrogen with chemical states reflecting combined sp(2) and sp(3) hybridization. Chemical analysis confirms nitrogen enrichment at levels consistent with the C3N4 stoichiometry and the estimated degree of stabilization. The possible mechanism(s) responsible for the stabilization of the beta-C3N4 phase are briefly discussed.